The present invention relates to laser transmitters of the type that are useful for surveying or spatial positioning at a construction site or elsewhere. Laser transmitters of the type that project a thin beam of laser light or a fan-shaped beam of laser light, and rotate the beam about a rotation axis, have been in use for a number of years at construction sites. Such transmitters can be used with manual surveying systems and also as a part of automated surveying systems. Laser transmitters of this type can also be used in spatial positioning systems that provide for control of earthmoving machines, and the like, to shape a construction site to a desired contour.
It is common to operate laser transmitters in a “dither” mode in which the laser beam is rapidly swept from side to side, illuminating only a small portion of an entire revolution. This technique permits a greater amount of power to be applied to a small portion of the beam rotation, illuminating a segment of interest with higher average power. Dithering involves reversing the direction of the transmitter motor after it has swept through a small segment of a complete rotation. For a transmitter to be capable of dithering has previously required that the transmitter include an accurate shaft angle encoder or similar device. It will be appreciated, however, that this will increase the cost of the transmitter significantly.
Other limitations have been encountered with prior art laser transmitters. Significantly, prior art transmitters have been limited in some respects with regard to the bearing support for the rotating pentaprism assemblies. A pentaprism has a useful property in that it will reflect outward a beam of light at ninety degrees to the path of the beam entering the pentaprism. Fluctuations in the orientation of the pentaprism will, however, cause the vertical position of the beam to fluctuate. When the beam fluctuates vertically, this in turn, cases the beam to be less than a reliable reference.
In summary, laser transmitters of necessity must be precise in operation. This need for precision, however, has resulted in transmitter constructions that are expensive to manufacture, that are somewhat complicated, and that are not as compact as might be desired. It is seen that there is a need, therefore, for a transmitter construction which overcomes the limitations of prior laser transmitters.